The present invention relates to an improved electrically powered driving mechanism for use on a bicycle which can be readily mounted onto a common bicycle without making any additional conversion work. It is particularly designed to improve the inefficiency of a conventional friction-type transmission of an electrically powered driving mechanism. It has a dual-purpose power transmitting device including a pair of driving wheels adapted for either frictional transmission or gear engagement transmission. Each driving wheel is divided into two sides, one side for friction transmission and the other side equipped with a plurality of consecutively spaced gear teeth for gear engagement transmission so that the driving wheels can be selectively assembled to make the driving mechanism to be either frictionally operable or gear drivable as long as the peripheral rims of a bicycle tire are provided with corresponding gear teeth. Besides, a dual-shaft electric motor provides power to the driving mechanism. Between the driving wheels and the dual-shaft electric motor is disposed a pair of shifting gear sets. The output of the dual-shaft electric motor can be varied in 3 options wherein the options include one output shaft being selectively locked and the other free; or both shafts free to output so as to provide 3 various torsion outputs to the driving mechanism in correspondence to operational conditions.
Generally speaking, current electrically powered driving mechanisms for bicycles available on markets are different in their ways of transmitting power to a bicycle. A first one is mounted to the axle of a wheel of a bicycle so as to permit power of a motor to be directly delivered to a wheel; a second one uses a motor in combination with the chain of a bicycle for delivery of power; the third employs a motor to drive the chain wheel which will drive in turn the hub of a wheel; the fourth one makes use of a motor to drive a friction wheel which is in pressing contact with a wheel of a bicycle so as to deliver power to a bicycle via friction
The above cited prior art electrically powered driving mechanisms are not easily adapted in a DIY (do it yourself) manner for a common bicycle. Moreover, such conventional driving mechanisms will interfere with a normal manual operation, causing a conventional pedal-operated mechanism to be blocked from smooth operation. As a result, a rider will easily feel exhausted when he or she manually pedals such a bicycle. Besides, the main problem in a friction-transmission electrically powered driving mechanism is that the normal frictional force is not effective enough to get a bicycle started from an initial rest position and the force is also not capable of driving a bicycle to climb a steep slope unless the friction means is adjusted to tightly press against a wheel of a bicycle with extra large pressure so as to obtain a maximum power via friction. As a bicycle moves down a sloped road, excessive friction force results in the loss of power in transmission and also serious abrasion of a wheel. In contrast, less pressure exerted between the friction means and a wheel of a bicycle can cause slippery invalid contact in operation, incapable of driving a bicycle to move forwardly.